The present invention relates to a navigational plotter and more particularly to a navigational aid employing a triangular plotter having pin-hole centered in a compass rose for plotting a true course on a chart or map.
The popular means of establishing a true course on deep water craft has been through use of a LORAN navigational system which gives a current position, finds a destination plot and computes a true course to follow, commonly all without reference to a chart or map. The most commonly used device for establishing a true course heading on a chart is a parallel ruler. The parallel ruler typically comprises a pair of straight edges arranged in parallel relationship by a pair of diagonal arms which are typically employed to move a course line, plotted on a chart or map, to a compass rose printed on said chart or map. Employment of this device involves first aligning one of the edges with a course line plotted on a chart. Then the straight edges are sequentially moved across the chart by alternately fixing one edge and moving the other relative to the initial fixed edge until one of the edges is aligned with the center of a compass rose on the chart. The heading would then be taken from the compass rose. This process necessarily involves relative slippage between the straight edges and the chart in the transferring of the parallel ruler across the chart. This may cause error in a plot. The amount of error is in direct relation to the amount of skill, the degree of care exercised and the amount of time expended. Also, the use of parallel rulers for establishing true course is typically accompanied by the use of dividers to determine distance by reference to the appropriate distance scale on the chart or map. Both instruments are adapted for use by a skilled navigator in a chart room on a large chart table rather than by a conning navigator in an open bridge or cockpit when underway.
Prior art navigational instruments used for determining true course heading on charts typically have been mechanically complicated, inconvenient to use, and more importantly, inaccurate when used at sea. Applicant is aware of prior art devices for calculating true course on a chart. Such prior art devices include the following U.S. Pat. Nos.:
______________________________________ 364,630 BOWER 3,377,706 SHRADER 1,289,905 POOR 3,535,788 SENA 2,545,935 WARNER 4,138,817 FROST ET AL. ______________________________________
While each of the references show some feature of the inventive combination, i.e., U.S. Pat. No. 4,138,817 Frost et al. shows a navigational aid used in conjunction with a map, the prior art references do not show a triangular plotter having a pin-hole centered in a compass rose for fixing a position with a sharp tipped drawing instrument nor do they integrate information furnished by a LORAN or GPS (Global Positioning System) navigational system to translate that information onto a chart to show the true course on the chart in relation to navigational hazards.
Accordingly, it is desirable to provide for a new and improved Navigational Plotter which is, quick, accurate and simple to operate (with a minimum of moving parts) which provides a cross-reference for Loran or GPS by displaying an independent course plot on a chart and which overcomes at least some of the disadvantages of prior art.